For producing wrapped slip tubes or spiral pipes from ribbon material that consists of metal at least in part, apparatuses are used comprising a profiling device, a bending device and a seam closing device. The profiling device forms matching seamed edges or brims of the ribbon material which, after deformation of the ribbon material in bending direction, are mutually inserted, and are pressed together by the closing device, that has cooperating closing wheels, to form a folded seam connection. The ribbon material engages helically a cylinder surface by a deforming surface in bending direction, the partial surface of a cylinder periphery, thus created, being called helical. For interconnecting the seamed edges, preferably a simple rim is inserted into a double rim, and subsequently these rims, which project from the outer surface of the tube, are closed and are preferably pressed against the outer surface of the tube. The folded seam connection extends helically about the wrapped slip tube thus produced. In order to be able to produce tube sections of a desired length, a cutting device, for example a rotating cutting-off disk or rotary shears, have to be provided.
From U.S. Pat. No. 4,567,742 an apparatus is known in which the metal ribbon is drawn by a pair of rolls through an arrangement of profiling rolls for forming the lateral edges or beads and for forming at least one stability increasing longitudinal fold, and is introduced into a bending and closing device having helical deforming surface and cooperating closing rolls. Between the pair of drive rolls and the bending and closing device, guide plates having longitudinal grooves for the edges and longitudinal folds of the ribbon material are used. As the guide plates, the deforming surface too is provided with grooves for the longitudinal folds. In order to be able to produce wrapped slip tubes of different diameter, the whole bending and closing device would have to be exchanged. If an apparatus according to U.S. Pat. No. 4,567,742 had to be used for producing tubes of a plurality of different diameters, a complete bending and closing device would have to be prepared for each diameter which requires much space for storing all bending and closing devices. Particularly in the case of large tube diameters, these bending and closing devices are heavy and cumbersome, and thus awkward when exchanging them. Also in solutions with curving or bending devices separated from the closing device, the deforming surfaces are often formed as heavy heads cast from aluminum.
An important disadvantage of this solution resides in that the intensive frictional contact of the ribbon material with the metal guide plates and the metal deforming surface results in wear of the guide and deforming surfaces as well as of the ribbon material. The ribbon material is subjected to an intensive frictional contact, and corresponding wear, also when passing the drive and/or profiling rolls. Wear of the metal results in optical spoiling of the surface of the produced wrapped slip tube. In addition, at least with zinc coated ribbon material, metal dust can be softened due to heat generated by friction and deposited, for example, on the closing rolls which affects the function of the rolls and increases maintenance expenditure. Also with ribbon material that is coated with plastic material, friction and heat result in undesirable damaging the tube""s surface and in adhering of coating material on the guide and deforming surfaces as well as on the closing rolls. In order to reduce wear and heating, parting oils in the form of water mixable cooling lubricants with combinations of mineral oils, emulsifying agents and other additives are used. A parting agent on the market is available under the trademark BLASOLUBE. In order to reduce friction, this parting agent is used in excess or as a bath so that the tube, thus created, entrains large quantities of parting agent out of the forming apparatus which results in pollution and/or higher expenditure for cleaning.
When ribbon material, coated with a white plastic material or consisting of polished stainless steel, is moved over guide and deforming surfaces that are of brass at least in part, brass dust causes clearly visible blackish spots on the wrapped slip tube. To clean these spots away using rags and a cleaning agent, excessive expenditure would be necessary. If, however, the dark spots remain on the tube, they affect the appearance of the tube which is undesirable on aerating tubes, for example, which are visibly mounted below a ceiling. Apart from the aesthetic spoiling, any damage of the plastic coating can lead to oxidation of the sheet metal protected by the plastic coating. Also if the ribbon material is uncoated, wear can result in an undesirable appearance and/or oxidation. Even on a ribbon of stainless steel, metal dust of the guide and deforming rolls can oxidize on the wrapped slip tube. For instance, the luster or a protecting oxide layer of the ribbon material can be affected by friction between the two metal surfaces. Accordingly, the aesthetic effect or the protection of the wrapped slip tube is diminished.
Apart from the problems resulting from wear, scobs or other solid particles getting between the guide surfaces and the ribbon material lead to faults or scratches on the surface of the wrapped slip tube. Particularly, if a cutting-off wheel is used as a cutting device, scobs will be generated when cutting a tube section off. Even if the cutting device does not produce scobs, an apparatus for producing wrapped slip tubes is often in a room where scobs are produced by other machines. Therefore, any scratching effect of such scobs on the wrapped slip tubes should be kept as little as possible.
DE 1 246 651 discloses an apparatus for producing wrapped slip tubes in which the deforming surface is extremely complicated in order to reduce friction between the ribbon material and the deforming surface. Four supporting plates are perpendicularly connected between two bearing plates. Each supporting plate supports 10 lamina of plastic material whose free surface areas form partial areas of a cylindrical deforming surface. These lamina have to have concave surfaces and to be mounted precisely to the bearing plates. Since the bearing plates are perpendicular to the axis of the tube to be produced, the lateral edges of the ribbon material supplied transversely to the axis and the closed folded seam connections extend transversely to the bearing plates and, thus over individual lamina, the lamina concerned being worn more severely than others. When introducing the front end of the ribbon material, its leading edge abuts laterally against the lamina which may result in damaging the lamina. Due to wear and damage, individual lamina have to be replaced again and again which involves undesirable high expenditure. In addition, the bearing plates have to be exchanged with high mounting expenditure whenever the diameter of the tube to be produced changes.
DE 2 017 383 describes an apparatus for producing wrapped slip tubes in which a closed plastic ribbon, running with the ribbon material, is arranged between the deforming surface and the ribbon material to prevent scratching of the tube""s outer surface. The arrangement of rolls for guiding the endless ribbon is expensive and liable to failure. In addition, this solution is not suitable, if spiral tubes of different tube diameter are to be produced. From U.S. Pat. No. 3,940,962, a solution is known in which plastic coatings are provided on flat guide plates so that the ribbon material can be supplied to the deforming surface under reduced friction. For deforming the ribbon material, rolls are used. The expenditure for introducing the front end of the ribbon material and for changing the tube""s diameter by changing the positions of the rolls is high. Although friction of the rolls is reduced due to the rolling motion, undesirable faults of the surface of the wrapped slip tube will occur nevertheless due to scobs or other solid particle getting between the rolls and the ribbon material.
U.S. Pat. No. 5,737,832 describes a method for producing wrapped slip tubes from a plurality of overlapping strips of ribbon material by a conventional deforming head. In order to prevent an undesirable deformation of the strips of ribbon material when initially bending them, it is suggested to provide guide plates of plastic material in the entering region of the deforming head. In the major part of the deforming surface, faults of the wrapped slip tube surface due to friction or scobs or other solid particles cannot be prevented. In order to be able to produce wrapped slip tubes of different diameters, the whole deforming and closing device, which is extremely massive, has to be exchanged which involves an undesirably high expenditure.
It is, therefore, an object of the invention to provide an apparatus for producing wrapped slip tubes of different diameter, and a bending device for it which are simple in construction and, in the case of ribbon material which is coated or has a sensitive surface, reduces undesirable pollution or damage.
Within the scope of the present invention, it has been recognized that metal dust can decisively be reduced if at least the deforming surface, and preferably also the guide surface, comprises a contact surface of plastic material. To this end, the deforming surface, and preferably also at least one guide surface, can be coated or produced from plastic material. The object according to the invention is attained by ribbon-shaped deforming surfaces having a contacting surface of plastic material. They are simple to exchange and may be provided for all tube diameters possibly required. Only small space is needed for storing ribbon-shaped deforming surfaces or forming ribbons. The preferred forming ribbons comprise a metal ribbon of spring steel coated with antifriction plastic material. In some cases, forming ribbons of plastic material, particularly of a monoplastic or a composite plastic material, are used. Composite materials comprise preferably glass fibers or carbon fibers.
When using a plastic coating, an extremely stable connection has to be made between the, preferably metal, bearing part and the coating. To this end, special adhesives which adhere particularly well to metallic surfaces can be used and/or an adhesiveness raising surface treatment of the bearing part can be performed. In suitable surface treatments, a roughening step is preferably effected by grinding and/or sandblasting. The plastic materials suited for coating have to ensure small friction coefficients in cooperation with the surface of the ribbon material. Such antifriction plastic coatings can be made, for example, of polyamide, particularly polyamide 11 (trademark RILSAN), or polyethylene, particularly of a PE ionomere (trademark Abcite) or chlorine trifluorethylene (CTFE), particularly E-CTFE (trademark HALAR). It is to be understood that other antifriction coatings, particularly teflon-like polytetrafluorethylene (PTFE) or polyperfluorethylene-propylene (T.FEP), can be used. The thickness of the plastic coating used is preferably in the range of 0.1-0.8 mm, and particularly in the range of 0.20-0.4 mm. Using coating thicknesses within these ranges, it can be ensured that the coated contact surfaces attain sufficiently long working times up to a complete wear of the coating. In some cases, worn off forming ribbons are coated anew with plastic material which can be effected with sensible expenditure and results in a minimum material consumption. Since metal dust is disturbing mainly with tubes that are either coated or consist of polished stainless steel, the use of coated forming ribbons can be restricted to these tubes. These specially sensitive tubes amount only to about 5-10% of the total production of a tube manufacturer. Therefore, the time of use of coated deforming surfaces or forming ribbons is relative short so that these coated forming ribbons need not to be replaced often. When processing zinc coated ribbon material, uncoated deforming surfaces may be used, because zinc undergoes an after-passivation at the damaged places. Moreover, scratches, due to forming flowers of zinc, are less visible on zinc coated material.
With today""s plastic material and shaping methods, forming ribbons, and preferably the guide surfaces too, can completely be produced of plastic material. To this end, both single-component parts, particularly from the above-mentioned antifriction plastic materials, and composite parts of different plastic materials are possible. In the case of composite materials, at least one fibrous material, particularly glass or carbon fibers, are used, for example for achieving high tensile strength. The fibrous material may be employed, e.g. as a reinforcement in an extruded or molded plastic part. In some cases, however, the fibrous material is used for manufacturing a yarn and then of a tissue. The tissue, in turn, may be employed as a reinforcement in a plastic part. Optionally, the tissue is coated with antifriction plastic material or is used directly as a forming ribbon. Plastic parts have less weight in comparison with coated metal parts. If the deforming surface of the bending device is not a rigid one, deformation motions, when changing the deforming surface, will lead to a lesser extent of damages or cracks in the case of a plastic part than in the case of a plastic coated metal part. Therefore, forming ribbons are advantageous which are substantially made of plastic material only.
If the forming ribbon, and optionally the guide surface too, comprises a contact surface of plastic material, no metal dust will be produced when the ribbon material moves along the contact surface. Plastic particles rubbed off in some cases is not dark and causes no oxidation. In addition, the surface of the ribbon material is prevented from being damaged. When plastic contact surfaces are used, the scratching action of scobs is also reduced, because scobs can be taken into the plastic material. Due to better sliding properties of plastic contact surfaces, it is even possible to use different lubricant. In particular, very small quantities of the lubricant, preferably in the form of a creep oil, may be applied so that neither the tube nor its ambiance are perceivably soiled. Preferably, a heavy duty cutting oil is used which comprises a mixture of mineral oil and hydrocarbon and, particularly, an ester. The lubricant available on the market under the name ISOLUBE is suitable to be applied.
The lubricant is not used in the form of a bath, but is preferably applied onto the surface of the ribbon material by an application sponge. Application is at least effected before deforming the ribbon material by means of the forming ribbon, but preferably already prior to profiling the ribbon material. To this end, the application device for applying the lubricant is preferably constructed in such a way that scobs are retained and cannot get between the ribbon material and an engaging contact surface. If a vaporizing lubricant is used, substantially no residues will remain on the tube.